: Virtually nothing is known regarding the transfer of sensory information from lumbar spinal levels to higher centers during the state of wakefulness or for that matter during other states such as quiet sleep and active sleep. The research described in this proposal is designed to utilize, for the first time, extracellular recording techniques in conjunction with procedures for drug microiontophoresis in the normally respiring cat to investigate the mechanism of suppression of antidromically identified lumbar sensory tract neurons, namely those comprising the dorsal spinocerebellar tract (DSCT), the spinoreticular (SRT) and spinothalamic tract (STT) that we have recently discovered to occur during naturally occurring behavioral states of active sleep. While each of these sensory systems project to the brain, they convey different forms of information. The DSCT principally relays afferent proprioceptive inputs important for sensorimotor integration while the SRT and STT principally relay tactile and nociceptive information to the brain. Detailed analyses will be performed of the spontaneous, glutamate-driven spike activity, and spike activity evoked by low-intensity stimuli applied to low-threshold primary afferents of DSCT, SRT and STT neurons recorded during the states of wakefulness, quiet sleep, the non rapid-eye-movement and rapid-eye-movement episodes of active sleep. An interdigitated series of combined microiontophoretic and extracellular recording studies are proposed to investigate whether a process of postsynaptic inhibition accounts for the suppression of these neurons during active sleep; and whether classical "fast" inhibitory amino acids, e.g., glycine and/or GABA, is the neurotransmitter responsible for mediating the active sleep-related suppression of transmission. The proposed studies will provide, in the chronic unanesthetized cat a comprehensive description and quantitative analysis of the basic electrophysiological characteristics of individual DSCT, SRT, and STT neurons during sleep and wakefulness. The studies proposed herein for DSCT, SRT and STT neurons should provide not only important new insights into the normal functioning of these distinct sensory tracts as a function of behavioral state and but also provide a complimentary data base for that which already firmly exists for the active sleep state-dependent suppression of somatomotor outflow. Finally, such data are essential if further insights regarding the fundamental nature of sleep and how the sleep state affects ascending sensory transmission in distinct sensory channels are to be realized which could prove useful in providing new insights toward understanding certain sleep disorders, e.g., REM-related paraesthesias and Behavior Disorder.